1. Field of the Invention
The present invention relates to semiconductor devices. In particular, the present invention relates to semiconductor devices formed using transistors and an operating method thereof. Further, the present invention relates to display devices including semiconductor devices and electronic devices including the display devices.
2. Description of the Related Art
In recent years, display devices such as liquid crystal display devices and light-emitting devices have actively developed. In particular, a technique for forming a pixel circuit and a driver circuit including a shift register circuit or the like (hereinafter referred to as an internal circuit) over the same insulator by using transistors formed using a non-single-crystal semiconductor has actively developed, because the technique greatly contributes to reduction in power consumption and cost, improvement in reliability, and decrease in frame. The internal circuit formed over the insulator is connected to a controller IC or the like provided outside the insulator (hereinafter referred to as an external circuit) through an FPC (flexible printed circuit) or the like, and its operation is controlled.
In addition, a shift register circuit including transistors formed using a non-single-crystal semiconductor has been devised as the internal circuit formed over the insulator (see Reference 1).
However, since an output terminal of the shift register circuit is in a floating state in a certain period, there has been a problem in that noise is easily generated in the output terminal and that the shift register circuit malfunctions due to noise generated in the output terminal.
In order to solve the foregoing problem, a shift register circuit whose output terminal does not enter into a floating state has been devised. For example, in Reference 2, a technique by which a shift register circuit is operated by so-called static drive has been proposed. In this case, since an output terminal of the shift register circuit does not enter into a floating state, noise generated in the output terminal can be reduced.
[Reference]
                Reference 1: PCT International Publication No. 95/31804        Reference 2: Japanese Published Patent Application No. 2004-078172        